1. Field of the Invention
The present invention relates to a simple-structured, compact planetary gear reduction device with a torque limiter function.
2. Description of the Prior Art
As a reduction device for reducing a rotation speed of a motor or the like, a planetary gear reduction device is generally known conventionally. The planetary gear reduction device can obtain a large reduction ratio and can be made compact, so it works effectively for various types of apparatuses to which it is attached.
FIGS. 1A and 1B are a plan view and a partially cutaway side view, respectively, showing the structure of one of conventional planetary gear reduction devices.
In this conventional planetary gear reduction device, as shown in FIGS. 1A and 1B, a stationary ring gear 46 is fixedly attached to a lower portion of a housing 43, and a motor 45 is mounted to a lower portion of the ring gear 46.
A sun gear 44 is fixedly mounted to a motor output shaft 45a rotatably supported at the center of the lower portion of the housing 43 and serving as an input shaft of the planetary gear reduction device. A planetary gear 47 meshes with the sun gear 44 through respective teeth formed on their respective outer circumferential surfaces, and meshes with the ring gear 46 through teeth formed on an inner circumferential surface of the ring gear 46. The planetary gear 47 is coaxially, integrally overlaid with another planetary gear 48. Three planetary gear pairs each constituted by the planetary gear 47 and the planetary gear 48 and rotatably attached to a carrier 51 and a carrier 52 provided on their lower and upper sides, respectively, are disposed around the sun gear 44. FIG. 1B shows one of the three planetary gear pairs.
An output shaft 41 is rotatably mounted at the center of an upper portion of the housing 43 through a stop ring 42 such that an axially down movement of the output shaft 41 is stopped. A flange gear 49 is fixed to the output shaft 41 in a press fit manner, and inner teeth 49a formed on the lower portion of the inner circumferential surface of the flange gear 49 mesh with teeth 48a formed on an outer circumferential surface of the planetary gear 48 (although not shown, the flange gear 49 meshes similarly with two other planetary gears 48 at different positions).
In the conventional planetary gear reduction device, when the motor 45 is driven to rotate the motor output shaft 45a, the sun gear 44 and then the planetary gear 47 are rotated. As the planetary gear 47 meshes with the ring gear 46 which is stationary, it moves around the sun gear 44 while rotating. As a result, the flange gear 49 is rotated through the planetary gear 48. Rotation speed of the motor output shaft 45a is reduced to that of the output shaft 41 in this manner.
The conventional planetary gear reduction device has the following problems.
When, for some reasons, an overload acts on an apparatus in which the planetary gear reduction device is equipped, power transmission must be disconnected to protect the motor and the planetary gear reduction device themselves. Also, when an overload acts on the apparatus due to, e.g., a human body touching with the apparatus, power transmission must be disconnected to assure safety.
However, the planetary gear reduction device according to the prior art does not have a torque limiter function. Therefore, a torque limiting mechanism for disconnecting power transmission depending on the frictional state of a clutch disk must be added to the output shaft of the planetary gear reduction device, which inevitably makes the structure become large. Even when a reduction device formed by combining gear trains without using a planetary gear reduction device is adopted and a torque limiting mechanism is mounted in it, the structure is complicated, thereby inevitably becoming large also.
The present invention has been made in consideration of the above circumstances in the prior art, and has as its object to provide a simple-structured, compact planetary gear reduction device with a built-in torque limiting mechanism, which can reliably disconnect power transmission when an overload acts on it.
In order to achieve the above object, according to the first aspect of the present invention, a planetary gear reduction device with a torque limiter function, comprises: a housing; an input shaft commonly served by an output shaft of a power source, rotatably supported by one of end of the housing, located at a radially central and axially lower portion of the housing and adapted to take in a torque from the power source; an output shaft rotatably supported by the other end of the housing, located at a radially central and axially upper portion of the housing adapted to take out the torque transmitted from the power source; a reduction gear train provided between the input shaft and the output shaft and comprising a plurality of gears meshing with one another; and a built-in torque limiting mechanism constituted in said reduction gear train, whereby when an excessive torque is generated in the output shaft, torque transmission from the input shaft to the output shaft is disconnected by an action of said torque limiting mechanism.
According to the second aspect of the present invention, the torque limiting mechanism of the first aspect comprises: a planetary bevel gear which is one gear of the reduction gear train; a flange gear mounted to the output shaft freely in an axial direction and fixedly in a circumferential direction and meshing with the planetary bevel gear through inner teeth formed on a bevelled lower end surface thereof; a compression means provided between an upper surface of the flange gear and a lower surface or an upper lid of the housing and adapted to constantly press the flange gear toward the planetary bevel gear, whereby when an excessive torque is generated in the output shaft, the planetary bevel gear and the flange gear are disengaged from each other by a reaction force generated between respective teeth of those gears meshing with each other so as to disconnect torque transmission from the input shaft to the output shaft.
According to the third aspect of the present invention, the torque limiting mechanism of the first aspect comprises: a flange gear mounted to the output shaft fixedly in an axial direction and freely in a circumferential direction; an internal gear formed on an upper surface of the flange gear; a declutch gear mounted to the output shaft freely in the axial direction and fixedly in the circumferential direction and adapted to mesh with the internal gear; and a compression means provided between an upper surface of the declutch gear and a lower surface of an upper lid of the housing and adapted to constantly press the declutch gear toward the internal gear, whereby when an excessive torque is generated in the output shaft, the declutch gear and the internal gear are disengaged from each other by a reaction force generated between respective teeth of those gears meshing with each other so as to disconnect torque transmission from the input shaft to the output shaft.
According to the fourth aspect of the present invention, the torque limiting mechanism of the first aspect comprises: a flange gear mounted to the output shaft fixedly in an axial direction and freely in a circumferential direction; a friction surface portion formed on an upper surface of the flange gear; a clutch disk mounted to the output shaft freely in the axial direction and fixedly in the circumferential direction and adapted to come in frictional contact with the friction surface portion; and a compression means provided between an upper surface of the clutch disk and a lower surface of an upper lid of the housing and adapted to constantly press the clutch disk toward the friction surface portion, whereby when an excessive torque is generated in the output shaft, the clutch disk and the friction surface portion are disengaged from each other by a reaction force generated therebetween so as to disconnect torque transmission from the input shaft to the output shaft.
In order to achieve the above object, according to the fifth aspect of the present invention, a planetary gear reduction device with a torque limiter function comprises: a sun gear fixedly mounted to an input shaft rotatably supported and located at a radially central and axially lower portion of a housing; a planetary gear meshing with the sun gear through respective teeth formed on their respective outer circumferential surfaces; a stationary ring gear having inner teeth on an inner circumferential surface thereof and meshing with the planetary gear through the inner teeth thereof; a planetary bevel gear coaxially and integrally mounted on the planetary gear to constitute a planetary gear pair; an output shaft rotatably supported and located at a radially central and axially upper portion of the housing; a flange gear mounted to the output shaft freely in an axial direction and fixedly in a circumferential direction and meshing with the planetary bevel gear through inner teeth formed on a bevelled lower end surface thereof; and means provided between an upper surface of the flange gear and a lower surface of an upper lid of the housing and adapted to constantly press the flange gear toward the planetary bevel gear, whereby when an excessive torque is generated in the output shaft, the flange gear and the planetary bevel gear are disengaged from each other by a reaction force generated between respective teeth of those gears meshing with each other so as to disconnect torque transmission therebetween.
In order to achieve the above object, according to the seventh aspect of the present invention, a planetary gear reduction device with a torque limiter function comprises: a sun gear fixedly mounted to an input shaft rotatably supported and located at a radially central and axially lower portion of a housing; a first planetary gear meshing with the sun gear through respective teeth formed on their respective outer circumferential surfaces; a stationary ring gear having inner teeth on an inner circumferential surface thereof and meshing with the first planetary gear through the inner teeth thereof; a second planetary gear coaxially and integrally mounted on the first planetary gear to constitute a planetary gear pair; an output shaft rotatably supported and located at a radially central and axially upper portion of the housing; a flange gear mounted to the output shaft fixedly in an axial direction and freely in a circumferential direction and meshing with the second planetary gear through inner teeth formed on a lower portion of an inner circumferential surface thereof; an internal gear formed on an upper surface of the flange gear; a declutch gear attached to the output shaft freely in the axial direction and fixedly in the circumferential direction and adapted to mesh with the internal gear; and means provided between an upper surface of the declutch gear and a lower surface of an upper lid of the housing and adapted to constantly press the declutch gear toward the internal gear, whereby when an excessive torque is generated in the output shaft, the declutch gear and the internal gear are disengaged from each other by a reaction force generated between respective teeth of those gears meshing with each other so as to disconnect torque transmission therebetween.
In order to achieve the above object, according to the eighth aspect of the present invention, a planetary gear reduction device with a torque limiter function comprises: a sun gear fixedly mounted to an input shaft rotatably supported and located at a radially central and axially lower portion of a housing; a first planetary gear meshing with the sun gear through respective teeth formed on their respective outer circumferential surfaces; a stationary ring gear having inner teeth on an inner circumferential surface thereof and meshing with the first planetary gear through the inner teeth thereof; a second planetary gear coaxially and integrally mounted on the first planetary gear to constitute a planetary gear pair; an output shaft rotatably supported and located at a radially central and axially upper portion of the housing; a flange gear mounted to the output shaft fixedly in an axial direction and freely in a circumferential direction and meshing with the second planetary gear through inner teeth formed on a lower portion of an inner circumferential surface thereof; a friction surface portion formed on an upper surface of the flange gear; a clutch disk attached to the output shaft freely in the axial direction and fixedly in the circumferential direction and adapted to come into frictional contact with the friction surface portion; and means provided between an upper surface of the clutch disk and a lower surface of an upper lid of the housing and adapted to constantly press the clutch disk toward the friction surface portion, whereby when an excessive torque is generated in the output shaft, the clutch disk and the friction surface portion that are normally in frictional contact with each other are disengaged from each other by a reaction force generated therebetween so as to disconnect torque transmission therebetween.
The above aspects have the following subsidiary aspects.
The sun gear, the planetary gear or the first planetary gear, and the ring gear are helical gears.
The compression means is a conical compression spring.
A plurality of planetary gear pairs are provided along an inner circumferential surface of the ring gear.
As is apparent from the above aspects, since the planetary gear reduction device with the torque limiter function according to the present invention includes a torque limiting mechanism which can be formed by the combination of the planetary bevel gear, the flange gear, and the compression spring in the first aspect, the combination of the internal gear formed on the upper surface of the flange gear, the declutch gear, and the compression spring in the second aspect, or the combination of the friction surface formed on the upper surface of the flange gear, the clutch disk, and the compression spring in the third aspect, it can be made simple in structure and compact, and can obtain a large reduction ratio while assuring safety.
Since the sun gear, the planetary gear or the first planetary gear, and the ring gear are helical gears, the torque can be transmitted smoothly, and noise as the disadvantage of the planetary gear reduction device can be decreased.
Since the compression spring is a conical compression spring, it can press the flange gear, the declutch gear, or the clutch disk with a minimum thickness in a well-balance manner.
The above and many other objects, features and advantages of the present invention will become manifest to those skilled in the art upon making reference to the following detailed description and accompanying drawings in which preferred embodiments incorporating the principle of the present invention are shown by way of illustrative examples.